A U.S. official and a congressional aide said Kerry will announce Tuesday that Feingold will assume the post focused, in part, on resolving turmoil in the Congo. They spoke on condition of anonymity because they were not authorized to disclose the information on the record before Kerry's announcement.

"I have a lot of respect for a lot of qualities of Russ, his intellect, his courage, his passion. But, with respect to this mission, chief among those qualities that are important right now is his expertise on Africa," said John Kerry, secretary of state.

Kerry said Feingold will focus his efforts on resolving the turmoil in the Congo where fighting between the government and rebels has resulted in the deaths of hundreds of civilians.

Congo's government and rebels have been negotiating in Uganda since December under a regional bloc called the International Conference on the Great Lakes Region.

The talks have often been set back by accusations over who is responsible for rampant violence in Congo's North Kivu province.

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